Inductance device with movable core having resilient disc for resisting core movement



Dec; 14, 1965 F. L. PAWLOWSKI 3,

INDUCTANCE DEVICE WITH MOVABLE GORE HAVING RESILIENT DISC FOR RESISIING CORE MOVEMENT Original Filed Feb. 23, 1960 FIG. 2

FIG I FRANK L. PA WLOWSK/ United States Patent INDUCTANCE DEVICE WITH MOVABLE CORE HAVING RESILIENT DISC FOR RESISTING CORE MOVEMENT Frank L. Pawlowski, Skokie, Ill., assignor to Motorola,

Inc., Franklin Park, Ill.,a corporation of Illinois Continuation of application Ser. No. 10,497, Feb. 23, 1960. This application July 12, 1963, Ser. No. 295,600

2 Claims. (Cl. 336-136) This application is a continuation of application Serial No. 10,497, filed February 23, 1960, and now abandoned.

This invention pertains. generally to movable core wherein core movement is restrained by a smooth, constant torque.

In electronic components such as intermediate frequency transformers and various coils, the inductance may be varied for tuning a circuit to a desired characteristic such as resonance. The windings of such intermediate frequency transformers and coils are usually wound around the periphery of a tubular form. A core or slug of permeable material is then positioned inside the form and held therein by threads or other means. By moving the core or slug it is possible to vary the inductance of the transformer or coil.

In structures generally used prior to the present time, difficulties have been encountered in maintaining the position of the core or slug inside the internal portion of the tubular member. The resistance to torque of the core to maintain a fixed position inside the tubular coil form has varied. To achieve an optimum tuning inductance, it is necessary that such inductance remain constant after the coil has been tuned and that the position of the core not be subject to variation due to vibration and other variable conditions such as changes in ambient temperature.

Thus, it is an object of the present invention to provide a variable inductance device which will remain fixed at a particular inductance after it is tuned.

Another object of the invention is to provide a variable inductance device having a core which responds to a constant torque when the core is rotated for positioning inside a tube.

Still another object of the invention is to provide a variable inductance device having a core which is simple, relatively low in cost, and may be tuned repeatedly without reducing the positioning accuracy.

A feature of the invention is the provision of an inductance device having a movable core with a disc made of resilient material bonded to the end of a tuning slug of permeable material.

Another feature of the invention is the provision of a variable inductance device which utilizes a resilient disc member bonded to the end of a threaded core which may be of any length.

A further feature of the invention is the provision of an inductance device having a coil with an internally threaded form, and a threaded core therein which is restrained by a constant torque when tuned for positioning in the coil form which may be made of material having different physical properties than those of the core device.

In thedrawing:

FIG. 1 is a bottom view of a coil mounted on a coil form with a slug and disc mounted therein; and

FIG. 2 is a cross-sectional plan view of FIG. 1 along line 2--2 showing the slug and disc bonded together to form the core.

In practicing the invention, a variable inductance device is provided having a coil wound on a form in which is provided an adjustable core which is restrained by a smooth, uniform torque when rotated inside the coil form. The core and coil form have complementary threads to provide adjustment of the position of the core within the coil form. A disc made from a resilient material such as cork may be bonded to the end of a tuning slug used for varying the inductance of the coil. The disc bonded to such slug is not threaded and the diameter of the disc is nominally that of the peak of the core threads. A hole may be provided through the entire length of the slug and disc to allow the coil to be tuned from both ends when desirable. The disc has uniform torque over wide dimensional tolerances and maintains uniform torque after many tuning operations. The resilient disc is integrally joined to the slug during manufacture to form a movable core structure. The coil form may be made of any suitable material and the resiliency of the disc provides. the proper fit with the coil form even with wide tolerances in manufacture. The disc may be used with a tuning slug of any length, and the resulting core structure is rugged and simple to fabricate.

In the drawing an inductance device is illustrated including a coil 10 wound on the periphery of coil form 12. A core or slug 14 is provided in the form 12 to change the permeability within the coil and thereby change the inductance thereof. The form 12 and slug 14 may have complementary threads so that the position of the slug in the form may be changed. A disc 16 is bonded to slug 14 to form a core structure. Disc 16 may be made of any resilient material such as cork, Coroprene, or leather and the thickness of disc 16 may be the same for all slug lengths. Slug 14 may be made from any permeaable material such as iron, ferrites, copper or aluminum.

The slug and disc may have a hexagonal hole 18 extending throughout the length of the core. The hexagonal center hole 18 allows engagement with the core to rotate and position the same by a tool entering from either end of coil form 12. Dics 16 is firmly bonded to slug 14 and the torque required to rotate the core structure is determined by the thickness and diameter of disc 16. Movement of the core structure including disc 16 and slug 14 provides very smooth tuning of the inductance of coil 10 regardless of the position of the core structure inside the coil form 12. The construction of the slug 14 is not dependent upon the physical properties of disc 16 or form 12. The slug can therefore be constructed to have the desired effect on the coil 10, and the disc can be separately designed to provide the desired torque to resist movement of the core structure. The disc will have substantially no effect on the inductance of the coil. Although a threaded core form 12 and a threaded slug 14 are shown, other forms can be used.

Thus, there is provided a variable inductance device having a core structure which provides excellent tuning under all types of atmospheric conditions, and the core structure remains fixed even when subjected to vibrations which may be encountered in mobile electronic equipment.

I claim:

1. An inductor device including in combination, a hollow cylindrical coil form having threads along the inside wall thereof, a coil wound on the external periphery of said coil form, and a core having a first portion with threads thereon for cooperation with said threads on said inside wall of said coil form for threaded movement of said core within said coil form, said first core portion being composed of metallic material which affects the inductance of said coil so that the position of said core may be changed to vary the inductance of said coil, said core including a second disc portion in direct engagement with and bonded to said first threaded portion, said second portion being formed of resilient non-metallic electrically insulating material having characteristics such that the inductance of said coil is substantially independent of the 3 4 position of said second disc portion with respect to said 2. The inductor device of claiml in which said second coil, said disc portion having an unthreaded outer surface disc portion is made of C0r0prene. with a diameter substantially the same as the peak diameter of the' threads of said first core portion so that said References Cited by the Examiner Elise portion compressed by said threads of said coil 5 UNITED STATES PATENTS orm, said disc portion causing. a substantially constant p value torque to resist threaded movement of said core 2,149,336 3/1939 Darnell 336136 insidesaid'cylindrical coil formgwhereby the position of 1 5/ 1943 Patl$chke et a1 said core may be'changed to varyithe inductance of said 2,838,738 6/1958 Anta'lek'et a1. 336-136 coil, and the position remains fixed during use so that 10 the inductance of said coil is thereby fixed. JOHN BURNS, Primary Examiner- 

1. AN INDUCTOR DEVICE INCLUDING IN COMBINATION, A HOLLOW CYLINDRICAL COIL FORM HAVING THREADS ALONG THE INSIDE WALL THEREOF, A COIL WOUND ON THE EXTERNAL PERIPHERY OF SAID COIL FORM, AND A CORE HAVING A FIRST PORTION WITH THREADS THEREON FOR COOPERATION WITH SAID THREADS ON SAID INSIDE WALL OF SAID COIL FORM FOR THREADED MOVEMENT OF SAID CORE WITHIN SAID COIL FORM, SAID FIRST CORE PORTION BEING COMPOSED OF METALLIC MATERIAL WHICH AFFECTS THE INDUCTANCE OF SAID COIL SO THAT THE POSITION OF SAID CORE MAY BE CHANGED TO VARY THE INDUCTANCE OF SAID COIL, SAID CORE INCLUDING A SECOND DISC PORTION IN DIRECT ENGAGEMENT WITH AND BONDED TO SAID FIRST THREADED PORTIN, SAID SECOND PORTION BEING FORMED OF RESILIENT NON-METALLIC ELECTRICALLY INSULATING MATERIAL HAVING CHARACTERISTICS SUCH THAT THE INDUCTANCE OF SAID COIL IS SUBSTANTIALLY INDEPENDENT OF THE POSITION OF SAID SECOND DISC PORTION WITH RESPECT TO SAID COIL, SAID DISC PORTION HAVING AN UNTHREADED OUTER SURFACE WITH A DIAMETER SUBSTANTIALLY THE SAME AS THE PEAK DIAMETER OF THE THREADS OF SAID FIRST CORE PORTION SO THAT SAID DISC PORTION IS COMPRESSED BY SAID THREADS OF SAID COIL FORM, SAID DISC PORTION CAUSING A SUBSTANTIALLY CONSTANT VALUE TORQUE TO RESIST THREADED MOVEMENT OF SAID CORE INSIDE SAID CYLINDRICAL COIL FORM, WHEREBY THE POSITION OF SAID CORE MAY BE CHANGED TO VARY THE INDUCTANCE OF SAID COIL, AND THE POSITION REMAINS FIXED DURING USE SO THAT THE INDUCTANCE OF SAID COIL IS THEREBY FIXED. 